Yeah, the learning curve of DF means just to get in the upper forums you need to have above average IQ and tons of patience.
I would definitely place the emphasis on patience. DF requires tons of it, and impatient people tend to be volatile, even if intelligent. This is probably the best thing this forum has going for it. Patience is a large part of 'chill' and everyone here seems to have a good amount of it.
We do have many radicals here (I myself am an anarchist), but we are patient with each other so it doesn't provoke as many episodes as in other places.
Toady and Threetoe are also great moderators, it seems. I haven't been here as long as many of you, but most moderators I've dealth with on other forums have been horrible. I've actually seen some really interesting cases of the tiniest bit of power completely changing a person's personality. Kinda scary.
Most of us are quite internet savvy, which also helps a lot.
I know one other forum that is almost as good as this one, while actually being much larger. ZBrushCentral. Awesome place. It has slightly more and worse outbreaks of uncivility than Bay12Forums, but I'd still place it second. Once again, it's a place where people go to share knowledge on a software that takes a lot of patience to learn, so there you have it.
I'd also like to point out that long long ago most of the internet was actually about as chill as this place is. I've been frequenting chat rooms and forums since '96, and things were way different back then. The general public believed that being on the internet meant you were either a nerd or a serial killer. So there was kind of a social taboo filter that made the internet mostly populated by decent, open-minded people. It started going downhill as socializing and finding hobbies online became more acceptable. I mentioned something about a chatroom in a high school classroom in '97, and the girl sitting next to me exploded in "OH MY GOD AREN'T YOU AFRAID THAT SOMEONE'S GOING TO FIND OUT WHERE YOU LIVE AND COME RAPE AND KILL YOU IN YOUR SLEEP LIKE IN THAT ONE MOVIE?!?!" Today I imagine that same girl is on the internet every day, still spewing ignorance.